Method for combusting exhaust gas with oxygen feed line

ABSTRACT

The exhaust gases stemming from an oil conveyance such as in a refinery or a chemical factory are flared with oxygen-containing gas fed into the flame, in particular with oxygen-enriched air with a high oxygen content or technically pure oxygen, so as to achieve as soot-free a combustion as possible that also generates less environmentally harmful emissions. The device for combusting exhaust gases is a combination of an exhaust gas pipe, an ignition device and an oxygen line, which is connected with an oxygen tank. The oxygen feed line is used in particular during operational malfunctions instead of a steam feed line or as an additional feed line when not enough steam is generated by the chemical plants.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority from German Patent Application DE102014013474.1 filed on Sep. 11, 2014 and European Patent Application EP 14003811.8 filed on Nov. 12, 2014.

BACKGROUND OF THE INVENTION

The invention relates to a method for combusting exhaust gases exiting from an exhaust pipe, wherein the exhaust gases are combusted with the formation of a flame at the outlet end of the exhaust pipe, as well as to an exhaust gas combustion device, which encompasses an exhaust pipe with an outlet end for the exhaust gas along as well as an oxygen feed line connected with an oxygen tank and an ignition device.

The combustion of exhaust gases is also referred to as flaring. Flaring is often used at refineries and in the chemical industry to eliminate exhaust gases that arise in particular during startup and shutdown operations and in pressure relief and evacuation equipment. Large quantities of gas can also exit in the event of malfunctions. Flaring is used where another application for the flared gas based on prior art or market demand makes no sense or is financially of no interest.

Exhaust gas combustion gives off a lot of sooty smoke, because not enough oxygen is available inside the flame for complete combustion. Several methods have been developed to achieve as soot-free a combustion as possible that generates less soot and other environmentally hazardous emissions, in which steam is introduced into the flame.

Such a method for exhaust gas combustion exhibits a flaring with steam supply, wherein the exhaust gas is ignited and combusted at the outlet end of a chimney-like pipe.

The steam is introduced into the flame at a high rate, and draws ambient air, and hence oxygen, into the inner core of the flame, thereby improving combustion. For example, such a method is known from the corporate brochure “Fackelsystem” (Flaring System) of SPG Prematechnik GmbH.

It is often the case that chemical plants generate large quantities of steam, which are available for combustion. However, given a nonvolatile lockout caused by an operational breakdown or unforeseen shutdown of the chemical plant, steam is also no longer available, and the air is no longer drawn into the flame due to a lack of steam, so that not enough oxygen is available inside the flame for a complete combustion, thereby resulting in intensive soot emissions.

Another method for combusting exhaust gas exhibits a feed line with an oxygen-fuel mixture in the flame, wherein the oxygen and fuel are supplied to a burner through two lines, and there mixed together. This produces a flame with a high temperature, wherein the oxygen-fuel ratio of the mixture is set based on the desired oxidation potential of combustion. For example, such a method is known from U.S. Pat. No. 3,864,072.

The object of the present invention is to indicate a method for combusting exhaust gases from a refinery or chemical factory, so that the exhaust gases can be combusted more effectively and completely and without soot, in particular in the event of malfunctions.

SUMMARY OF THE INVENTION

This object is achieved by a method for combusting exhaust gases, wherein the exhaust gases exit from an exhaust pipe, and are combusted with the formation of a flame at the outlet end of the exhaust pipe, wherein an oxygen-containing gas with an oxygen content exceeding 22% is introduced into the flame.

According to the invention, there is further provided a device for combusting exhaust gases which comprises an exhaust gas pipe with an outlet end and a feed line along with an ignition device, wherein the feed line is designed as an oxygen feed line, and connected with an oxygen tank.

In the invention, an oxygen-containing gas with an oxygen content exceeding 22% is introduced into the exhaust gas, so that enough oxygen is available inside the flame, and the exhaust gases are combusted more efficiently and completely, and without soot.

The exhaust gases preferably originate from a refinery or chemical factory. For example, the exhaust gases arise during a material conversion process or are no longer usable gaseous waste products, e.g., from internal combustion engines or technical incinerators. The invention is used in particular when the exhaust gases are harmful and dangerous to humans and/or the environment.

Preferably used in the method according to the invention is an oxygen-containing gas, in particular oxygen-enriched air with an oxygen content exceeding 30% v/v, exceeding 50% v/v, exceeding 80% v/v, or technically pure oxygen with an oxygen content exceeding 95% v/v or exceeding 99% v/v, so that the exhaust gas reacts more efficiently with the oxygen, and a complete combustion takes place. Supplying the oxygen improves the combustion of the carbon compounds present in the exhaust gas. The advantage to this is that less soot is formed, and nitric oxides in the exhaust gas are also reduced.

The method is preferably used when the exhaust gas contains hydrocarbons or other toxic, environmentally harmful or unhealthy substances, e.g., carbon monoxide, nitrogen oxide, sulfur oxide. For example, the hydrocarbons or other toxic substances arise in a refinery or in a chemical factory when carbon-containing fuel is incompletely combusted.

In the method according to the invention, the oxygen-containing gas is further relayed through a nozzle and brought inside the flame, preferably at a higher speed that preferably measures 0.1 to 3 times the speed of sound, especially preferably 0.5 to 2 times, most especially preferably 0.8 to 1.2 times the speed of sound. The speed is determined using the nozzle cross section and supply pressure, adjusted via the upstream pressure during startup, and set prior to installation of the system. As the speed increases, more ambient air is also drawn in, and thus more oxygen is guided into the inner core of the flame, thereby improving exhaust gas combustion. Injecting the oxygen-containing gas into the combustion zone generates turbulences in the flame, so that the air is mixed with the exhaust gas for smokeless combustion.

In the method according to the invention, the oxygen-containing gas is preferably upwardly introduced into the flame in proximity to the outlet end of the exhaust gas pipe at an angle of 0 to 45 degrees, preferably 10 to 30 degrees to the vertical, so as to maintain the flame even during exposure to crosswinds.

The oxygen-containing gas is preferably sprayed into the flame, so as to draw in additional ambient air and convey more oxygen to the inner core of the flame.

The oxygen feed line is preferably used during operational malfunctions when not enough or no steam is generated, e.g., given a nonvolatile lockout caused by an operational breakdown or unforeseen shutdown of the chemical plant. The exhaust gases can then also be combusted efficiently and without soot even without supplying steam.

The combustion device according to the invention encompasses an exhaust pipe with an outlet end for the exhaust gas, as well as a feed line and an ignition device, which ignites the gas mixture from the exhaust pipe and generates a flame, e.g., pilot burner, ignition electrode, gas igniter, wherein the feed line is designed as an oxygen feed line, and connected with an oxygen tank.

The device is preferably built in such a way that the oxygen feed line ends in proximity to the outlet end of the exhaust pipe, so that the oxygen-containing gas is introduced into the flame, during which air is drawn into the combustion zone and generates air turbulences, so as to mix the air with the exhaust gas for a smokeless combustion.

The oxygen feed line is preferably built at an angle of 0 to 45 degrees, preferably 10 to 30 degrees to the vertical, so that the flame is maintained during exposure to crosswinds.

A nozzle is preferably used for spraying the oxygen into the flame, so as to draw in additional ambient air and convey more oxygen into the inner core of the flame. A nozzle is understood to mean a length of pipe with a narrowed cross section and/or expanded cross section and/or other complex shapes, in particular a Venturi nozzle.

The oxygen tank is preferably a liquid tank, wherein the liquid oxygen from the liquid tank is converted into gaseous oxygen with an evaporator, and introduced into the flame through the outlet end of the oxygen feed line.

The oxygen feed line is preferably connected with an oxygen tank by way of a valve, which serves to release the fixed oxygen quantity, and is designed as a shutoff valve. In order to increase the oxygen quantity, correspondingly more systems are installed in parallel, which can provide the oxygen via several oxygen feed lines.

To reduce the vulnerability of the flaring system to failures, the supplied quantity of oxygen is also often not regulated with a control valve, and the maximum quantity of oxygen available is always used.

In addition, a second line is preferably used in the device, so that the exhaust gases can also be combusted with a gas other than oxygen, in particular steam, when enough other gas from the chemical plant or chemical factory is available to draw enough air into the combustion zone of the flame.

BRIEF DESCRIPTION OF THE DRAWINGS

Additional advantages and features of the present invention will be explained in the following description of the figures based on the following figures shown here as:

FIG. 1 is a schematic view of a device according to the invention, and

FIG. 2 is an alternative embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 presents a schematic view of a device according to the invention for combusting exhaust gases. The device consists of an exhaust pipe 1, an ignition device 2 and an oxygen feed line 3, which is connected with an oxygen tank 4. The exhaust gases, for example which come about in a refinery or in a chemical factory, exit from the exhaust pipe 1, and are ignited by the ignition device 2 with the formation of a flame.

An oxygen-containing gas, in particular oxygen-enriched air with an oxygen content exceeding 30% v/v, exceeding 50% v/v, exceeding 80% v/v or technically pure oxygen with an oxygen content exceeding 95% v/v or exceeding 99% v/v, is introduced into the flame through the oxygen line 3, wherein the oxygen is introduced from a liquid oxygen tank 4 by way of a valve 5. The valve 5 is used to release the fixed quantity of oxygen, and is designed as a shutoff valve. In addition, it is easier to provide oxygen in a tank system than to generate steam, in particular when there is a malfunction.

In order to increase the quantity of oxygen, correspondingly more systems were installed in parallel, which can provide the oxygen by way of several oxygen feed lines. Since flaring systems must not be vulnerable to failure, a valve is not used for regulation purposes, and the maximum quantity of oxygen available is always used.

The oxygen feed line according to the invention introduces more oxygen into the inner core of the flame, resulting in the advantage of a complete combustion and less soot formation. The oxygen feed line is preferably located upwardly in proximity to the exhaust pipe at an angle of 0 to 45 degrees, preferably 10 to 30 degrees to the vertical, so as to maintain the flame during exposure to crosswinds. The oxygen-containing gas is preferably sprayed into the flame with a nozzle, in particular a Venturi nozzle, so as to additionally draw in more ambient air and convey more oxygen into the inner core of the flame. For example, the method according to the invention can be used to introduce the oxygen-containing gas at the speed of sound or a similarly higher speed, wherein more ambient air is drawn into the combustion zone with a rising speed, where turbulences are generated, resulting in an efficient and smokeless combustion.

FIG. 2 shows an alternative device according to the invention. Identical elements are provided with the same reference numbers in both figures. A second line 6 is additionally provided in the device according to FIG. 2. In normal cases, the exhaust gases are combusted while supplying a gas other than the oxygen-containing gas, in particular steam. A normal case or operation is when enough of the other gas can be generated in the chemical plant or be otherwise provided, so that enough air is drawn into the flame by supplying the other gas.

In the event of malfunctions, e.g., given a nonvolatile lockout caused by an operational breakdown or unforeseen shutdown of the chemical plant, the other gas can often no longer be provided in sufficient quantity. In this case, additional oxygen-containing gas is introduced into the flame from the oxygen feed line 3. Therefore, both the oxygen-containing gas and the other gas, for example steam, are supplied to the flame.

However, if the other gas is not even available for exhaust gas combustion at all during malfunctions, only the oxygen-containing gas is introduced into the flame by way of an oxygen feed line 3, so that the exhaust gases can be combusted completely and without soot. 

What I claim is:
 1. A method for combusting exhaust gases existing from an exhaust pipe, characterized in that an oxygen-containing gas with an oxygen content exceeding 22% is introduced into a flame at an outlet end of the exhaust pipe.
 2. The method according to claim 1, characterized in that the exhaust gas is formed while conveying oil, in a refinery or in a chemical factory.
 3. The method according to claim 1, characterized in that oxygen-enriched air with an oxygen content exceeding 30% v/v is used as the oxygen-containing gas.
 4. The method according to claim 3, characterized in that oxygen-enriched air with an oxygen content exceeding 50% v/v is used as the oxygen-containing gas.
 5. The method according to claim 3, characterized in that oxygen-enriched air with an oxygen content exceeding 80% v/v is used as the oxygen-containing gas.
 6. The method according to claim 3, characterized in that oxygen-enriched air with an oxygen content exceeding 95% v/v is used as the oxygen-containing gas.
 7. The method according to claim 3, characterized in that oxygen-enriched air with an oxygen content exceeding 99% v/v is used as the oxygen-containing gas.
 8. The method according to claim 1, characterized in that the exhaust gas contains hydrocarbons or other toxic substances.
 9. The method according to claim 1, characterized in that the oxygen-containing gas is introduced at a speed that measures 0.1 to 3 times the speed of sound.
 10. The method according to claim 9, characterized in that the oxygen-containing gas is introduced at a speed that measures 0.5 to 2 times the speed of sound.
 11. The method according to claim 9, characterized in that the oxygen-containing gas is introduced at a speed that measures 0.8 to 1.2 times the speed of sound.
 12. The method according to claim 1, characterized in that the oxygen-containing gas is upwardly introduced into the flame in proximity to the outlet end of the exhaust gas pipe at an angle of 0 to 45 degrees to the vertical.
 13. The method according to claim 1, characterized in that in the event of a malfunction both the oxygen-containing gas and an additional gas are introduced into the flame.
 14. The method according to claim 13, characterized in that the additional gas is steam.
 15. A device for combusting exhaust gases, which encompasses an exhaust pipe with an outlet end for the exhaust gas along with a feed line and ignition device, characterized in that the feed line is an oxygen feed line and connected with an oxygen tank.
 16. The device according to claim 15, characterized in that the oxygen feed line ends in proximity to the outlet end of the exhaust gas pipe.
 17. The device according to claim 16, characterized in that the oxygen feed line exhibits an angle of 0 to 45 degrees to the vertical.
 18. The device according to claim 17, characterized in that the oxygen feed line is provided with a nozzle.
 19. The device according to claim 18, characterized in that the nozzle is a Venturi nozzle.
 20. The device according to claim 15, characterized in that the oxygen tank is a liquid tank.
 21. The device according to claim 15, characterized in that a valve is located downstream from the oxygen tank.
 22. The device according to claim 21, characterized in that the valve is a shutoff valve.
 23. The device according to claim 15, characterized in that an additional feed line is provided. 